Chronic rhinosinusitis (CRS) is a significant health problem in the United States. It has been hypothesized that a common etiologic pathway may involve transient or chronic alterations to the sinonasal epithelial barrier perhaps allowing passage of agents that perpetuate a cycle of antigen exposure, increased cytokine release, and inflammation. There are two histopathologic subtypes of CRS, one without and one with nasal polyps (CRSsNP and CRSwNP respectively). The cellular and molecular mechanisms that underlie CRNsNP and CRSwNP remain poorly understood. A recent study published in Nature from the lab of our collaborator Dr. Dean Li demonstrated that the inflammatory cytokine interleukin-1 beta (IL-1) activates the ADP ribosylation factor nucleotide exchange factor (ARNO)-ADP-ribosylation factor 6 (Arf6) pathway independently of NF-?B to reduce inter-cellular junction protein cell surface localization in the vasculature. Our preliminary studies suggest that one can enhance sinonasal epithelial barrier stability and reduce indicies of CRS through targeted inhibition of the ARNO-Arf6 pathway. We hypothesize that as previously demonstrated in the vascular system, Arf6 is a central regulator of cytokine-induced destabilization of sinonasal epithelial junction protein cell surface localization and barrier permeability. We hypothesize that the sinonasal epithelial cell barrier in CRSsNP and CRSwNP patients is destabilized at baseline as well as through inflammatory cytokine signaling via increased Arf6 activity, and that inhibition of ARNO-Arf6 signaling will restore stability in both settings in an NF-?B-independent manner. Lastly, we hypothesize that inhibition of ARNO-Arf6 signaling will increase barrier stability and will reduce indicies of CRS. To test these hypotheses we will initially, in aim 1, examine sinus mucosa and characterize baseline and cytokine-induced differences in SNEC junction destabilization in patients without chronic sinusitis, CRSsNP and CRSwNP. We will also determine whether inhibition of Arf6 activity stabilizes the sinonasal epithelial barrier and reduces cytokine-induced barrier permeability. We will also determine whether inhibition of ARNO-Arf6 acts independently of NF-?B signaling in cytokine-treated SNECs. In aim 2, we will utilize genetically modified mice and the ovalbumin mouse model of CRS to determine whether stabilization of the epithelial or endothelial barrier through genetic deletion of the ARNO-Arf6 pathway reduces sinusitis. Fundamentally the studies proposed here seek to understand the pathologic role that barrier instability and permeability play in CRSsNP and CRSwNP and to evaluate the ARNO-Arf6 pathway as a therapeutic target. As elucidation of the barrier stabilizing effects of inhibition of the ARNO-Arf6 system has largely been limited to stabilizing the vascular barrier, this proposal has potential significance and applicability beyond sinusitis to other conditions affecting epithelial barrier stability.